sherwin



Jan. 24, 1956 wm 2,731,878

METHOD OF AND APPARATUS FOR DETERMINING THE MICROCONSTITUENT CONTENT OF METALS Filed March 10, 1954 2 Sheets-Sheet l his Afforney.

Jan. 24, 1956 H s w ,73l,878

METHOD OF AND APPARATUS FOR DETERMINING THE MICROCONSTITUENT CONTENT OF METALS Filed March 10, 1954 2 ShQEtS-ShGG 2 //v vs/v TOR. LEO H. SHERWl/V,

his Affomey.

United States Patent" Ofifice 2,731,878

Patented Jan. 24, 1956 1 2,731,878 volume of a given microconstituent in a metal specimen is equal to the percent of the area of a polished plane METHOD OF AND APPARATUS FOR DETERMIN- ING THE MICROCGNSTITUENT CONTENT OF section of the specimen which is occupied by such con METAL stituent It has also been established that the percent by volume of the constituent in the sample is equal to Leo H. Sherwin, Pittsburgh, Pa., assignor to United States the percent of a straight line taken at random across the Steel Corporation, a corporation of New Jersey surface of a polished plane section Which coincides with the total length of the constituent grains lying along such Apphcanon March 1934 Sena! N 4l5271 line Both the area percentage and the linear percentage 4 Cl i s, (Ci. 88--14) occupied by the constituent in a polished plane section This invention relates as indicated to a method of and representing Conventional PractiCe Since it is quicker and apparatus for determining the microconstituent content accurate However, F Y Of cohventlohfll f metal specimens prepared by metanographic tech practicesbased on a determination of the linear perniques centage is dependent on the visual perception or the More spgcifically this invention is directed to {he metallographer, and several determinations must be made problsm f Obtaining a quantitative analysis f the from which an average 18 taken to reduce the margin of stituents in metals, particularly steels and alloys thereof errol a w two more elements are alloyed or c0mp0und A further ob ect or this invention is, accordingly, to ed together and the resulting alloy is frozen from a melt Provlde a method of apparhtus for det3rhhh1hg the the resulting mstal will not always be a homogeneous percentage of micioconstituents in a metal in which th stance. in most instances (such as stee the me al will a cculacy m h detenhmahoh not dependent on the be composed of a semi-orderly agglomeration of con- Vsual P P the opfiratoh stituents each of which is associated with one of the basic 6 ehlect t0 Pr e method of and apparatus elements and each of which contributes certain charac- Ior recommg h Intensity F hght emlfled by an Illumiteristics to the properties of the whole. Furthermore, in Hated repl'oducufm of a P F and ethhed sul'fac'i of most metals (again steel is an example) hast treatment a test Inetal specimen along a line extending transversely of the solid material will change its constituents in one of the fnummated f or more Ways such as type, size and distribution. Since A further Ohleit 15 to Provide h apharahls and it recognized that the propel-ties of a metal are Clam}, methoo of the character ust referred to in which the recallied to the type and distribution of ts constituents the 0rd of the lmear fight Intensity of the luuhhhafed study of microconstituents is basic to research and stu y Producuoh 13 (named by Phomelecmcahy Scahhlhg the of most metals. reproductloh- While the Conventional mstauograph has bean Other ob ects and advantages of the invention will be veloped extensively for the purpose of examining the arapparent fromfile Q P descnptlons rangement and distribution of the constituents of metals In the g Preferred embodl and for making microstructural studies thereof, the probof the in f showlhgi lem of determining the quantity of selected ones or all of 1 1S a d1 agammanc P f W of an apparatus the constituents in any given metal has continued to be emliodymg h prmclplfi? of mventlohi a source of considerable trouble. Conventional prac- Figure 2 apefipecfive View of a Portlon of the P" tices for making such determinations are not only tedious paraius shown figure 15 and difiicult but consume considerable time in ariivin Figure 3 1S a magrammatlc Showmg the essehhal at a determmatmn Whlch can be sald to be reasonably electrical components of the photoelectric scanmn and accurate. Wi h the diificulties of conventional practice in recording shown In Floures 1 and 2, and mind, this invention has as its principal ob ect the provi- Figure 4 1s a pamal Plan View of a record tape sion of a method and apparatus Whlch faclhtate the ing a record thereon of a schematic nature foi the purr pose of illustrating the manner in which the percentages To this end, and in a manner to be described, an illumiof mict-gconstituents in a metal samp 1e are detprmined' nated and microscopically enlarged reproduction of an In Flgure the fiissenfial .parts of a conventional metaletched surface of a metal specimen, which may be either lograph for producing a mlcroscoplcauy enlarged reproa photograph or reflected image 18 examined electricaldaemon Or Image of a Pollshed and etched surface of a thereof, and from which the microconstituent content 1 dslgnates a test metal Specimen 1S mounted m of the Specimen can be calculated a table 2 and has an upwardly facing surface 3. The In Conducting mtauographic Studies of a metal Specl; surface 3 1S polished and etched in the conventional man men, a scratch-free surface of a metal specimen is pre Her for metallograph ic observation prior to mounting the pared by Cutting, grinding, and polishing, which is than specimen 1 in the table 2. Parallel rays or light are etched in a conventional manner. After etching, the con- Projected against the sturface by lens elements 5 and 6 stituents have diiferent light refiectivities which render from a i 7 which l'ecelves Source 8 their arrangement and boundaries visible to the metallogby Way CI 3 lens 9 and a Plate 10 having a light passing rapher. it is thus possible for the metallographer to a 11 thereih- Reflected light from the Surface 3 examine the distribution and arrangement of the constitu- 6O is delivered by the lens elements 5 and 6 through h ents, for example, cementite, ferrite, pearlite, austenite, reflector 7 to a Prism Thh Prism 12 in turn delivers m i l t d t l specimens the reflected light to the bellows 13 of a metallographic While the arrangement and distribution of the concamera having a ground glass screen 14 (see Figure 2) 3 includes a focusing 15 which receives the surface 3 transmitted showings of the components of minated reproduction of aportion of the object surface 3. The parts .of the apparatus thus far referred to for producingthe illuminated image on the screen 14 are conventional.

A record of the intensity of light emitted by the screen 14 along a line extending transversely thereof is produced .by a scanning unit designated as a Whole by the numeral 16 and a recording instrument 17. The units 16 and 17 are vconventional types which areproduced commercially in a number of forms suitable for the purposes of this invention. Accordingly, it will be understood that the these units in the drawpurpose of explaining the that such showings are the conings are schematic for the principles of this invention, and not intended to illustrate the precise structure of ventional apparatus actually employed.

The scanning unit 16 comprises a light excluding enclosure or housing 18 having a photoelectric cell 19 mounted therein and an aperture 2% through which light is delivered to the cell 19. The photoelectric cell may be either a self-generating photo-voltaic cell or a phototube having an external energizing source of potential. The housing 13 is mounted on a table 21 with the aperture 2% facing and positioned closely adjacent the surface of the screen 14 so that the light projected against the cell 19 will be dependent upon the intensity of the light emitted by the portion of the screen 14 opposite which the aperture 26 is located. The housing 18 is mounted on the table 21 by ways 22 which provide for a guided rectilinear movement of the housing 18 and its aperture along a line extending transversely of the screen 14. The housing 13 has a micro-drive including a screw 23, a speed reduction transmission 24 and a variable speed electric motor 25 for moving it at a controlled rate of speed along the table 21 and laterally of the screen 14, the housing having a drive nut (not shown) connecting it to the screw 23 for traverse movement thereby in the manner of conventional screw machines.

The recording device 17 is a conventional instrument having a moving tape 27 and a marking device 23 operated by a galvanometer type of mechanism for recording changes in electric potential or an electrical force thereon. As shown in Figure 3, the tape 27 is mounted on spaced reels 29 and 30 and is driven in the direction indicated by the arrow by a variable speed electric motor 31 or other prime mover connected to the reel 39. The marking device 23 is actuated linearly and transversely with respect to the tape 27 by a solenoid 32 against the action of a biasing spring 33 in accordance with current variations in its operating coil 34. The terminals of the coil 34 are connected with the output terminals of an amplifier 35 which has its input terminals connected in circuit with the photoelectric cell 19. As the light emitted by the screen 14 and projected through the opening 20 against the photoelectric cell 19 varies with movement of the housing 18 across the face of the screen 14, a corresponding variation in the voltage produced by the cell 19 is effected. This changing voltage is amplified in the amplifier 35 and produces a changing current in the coil 34 which is effective through the solenoid 32 and biasing spring 33 to move the marking device 23 transversely with respect to the movement of the tape 27 by amounts corresponding to the varying intensity of the light projected through the opening 20. The movement of the tape 27 in the direction of the arrow by the motor 31 will of course be related to the movement of the scanning unit 16 by the motor 25, and the linear length of the line 35 along the length of the tape 27 will-thus have a predetermined relation tothe traverse movement of the scanning uanit across the face of the screen 14, and this relation may be varied readily by adjusting the .relative speeds of the meters 25 4 and 31. The lateral deflections of the line 35 by transverse movements of the marking device 28 will of course afford an indication of the microconstituents scanned during the scanning movement of the unit 16.

The manner in which the record on the tape 27 provides an indication of the microconstituent scanned by the unit 16 along a line transversely of the microscopically enlarged reproduction on the screen 14 and from which the percent by volume of any given microconstituent may be determined will be best understood by reference to Figure 4-. in this showing, the line 35 on the tape 27 has been drawn for the purpose of illustrating the principles of the invention, and it will be understood accordingly that this line is not one which was obtained by'a use of the invention. Before referreing further to Figure 4, it will be recalled that the various constituents have difierent intensities of illumination in the microscopically enlarged reproduction of an etched surface of the specimen on the screen 14. By reason of the different intensities of illumination of the constituents, each constituent will cause a difierent deflection of the marking device 28 as the aperture 24 of the scanning unit moves over a particle of such constituent. Assuming that the metal specimen is comprised of three constituents, which will be designated here generally by the letters a, b, and c, the line 35 along the length of the tape 2'7 will be comprised of a series of peaks a, b and 0, such peaks being due to the difierent intensities of illumination from such constituents as the particles thereof are examined by the scanning unit. In Figure4, the straight portions 49 and 41 of theline 35 represent the mark made by the device 28 just before and just after the scanning unit moves over the enlarged reproduction as, for example, when the unit 16 is scanning the frame along the edges of the glass screen 14. The linear length of the tape between the dotted lines 42 and 43 represents the total length of the reproduction scanned. As the scanning of the reproduction is started at the line 42, the record line 35 rises to a peak a which is determined by the intensity of illumination from the constituent a. At the line 44, the record line 35 drops to a lower peak b which isdetermined by the intensity of illumination from the constituent b. The distance between the lines 42 and 44 represents the length of the first particle of the constituent a. At the line 45, the record line 35 starts increasing, and the distance between the lines 44 and 45 represents the length of the first particle of the constituent b which is scanned. Between the lines 45 and 46, the record line 35 rises to a second peak a and the distance between the lines 45 and 46 gives a representation of the length of the second particle of the constituent a. Between the lines 46 and 47, the record line drops to an intermediate peak 0, and the distance between these lines similarly represents the length of a particle c. In like manner, the distance between the lines 47 and 48 give an indication of the length of the next particle of the constituent a. Since the record line 35 iscomprised of a series of peaks a, b and 0 along its length, it provides a record of the number and lengths of the particles of the constituents a, b and c along the line of the reproduction traversed by the scanning unit 16. The percent by volume of such constitucnts may be readily and accurately determined by adding together the'distances between the beginning and end of each of the peaks along the record line 35. The total thus obtained is divided by the linear distance between the lines 42 and 43 and the quotient gives the percent by volume of each constituent in the specimen examined. The constituents designated by the letters a, band 0 above may, for example, be cementite, ferrite, and austenite in a steel comprised essentially of these constituents.

In the above description, the microscopically enlarged reproduction has been described as being produced on the ground glass screen 14 of a conventional metallographic camera. 'HoWever'it 'will be understood that the prin- 2,781,878 5 ciples of the invention are applicable to other types of electrical intelligence in the form of an electric force illuminated metallographic reproductions. For example, varying with the intensity of illumination along said line. the reproduction scanned by the unit 16 may be a photo- 2 A method of determining the metallographic conmicrograph and in such case, the unit 16 would scan stituent content of a metal specimen which comprises the light reflected from the face of the photograph from 6 producing an illuminated reproduction of an etched sura source of light trained on its surface. In like manner, face of the specimen, electrically scanning the intensity a negative of the photograph could be used and in this of illumination from each point of said reproduction alon case the negative would be positioned between a source of a line extending tiansveisely thereof to produce electrical light and the scanning unit 16. intelligence in the form of an electric force varying with It will also be understood that the principles of the 10 the intensity of illumination along said line, and record invention are applicable to enlarged reproductions in ing the variations in said electric force to provide a record which the constituents are shown in difl'erent colors. In of microconstituents of said specimen. such case, the scanning unit by the use of suitable colored 3. A method of determining the metallographic confilters can be made responsive to a single microconstituent content of a metal specimen which comprises prostituent, 5 duciiig an illuminated reproduction of an etched surface In the above description, traverse movement is imof the specimen, moving a photoelectric scanning unit parted to the scanning unit 16 with respect to the microrelatively with respect to said reproduction along a line scopically enlarged reproduction of the metal specimen extending transversely thereof to obtain an electric force eing examined However, it will be understood that the varying with the intensity of illumination from each point scanning unit 16 may be made stationary and traverse of said reproduction along said line, recording the variamovement may be imparted to the enlarged reproduction. tions in said electric force, and using said recording to A modification for this purpose is shown in Figure 1 determine the metallographic constituent content of the wherein the specimen mounting table 2 18 shown as having specimen. a nut 50 engaged with a screw 51 which is operated by an 4. In apparatus for determining the microconstituents electric motor 52 through a speed reduction transmission 25 of an illuminated reproduction of an etched metal speci- 53. Movement of the table 2 by its micro-drive will remen, a recording instrument having a moving tape, a sult in a shifting image on the ground glass screen 14. marking device mounted for movement transversely of n the use of this modification the housing 18 is prefersaid tape, and means responsive to a varying electrical ably held in the position shown in Figure 1 with its aper- I force for actuating said maiking device, a scanning unit ture 20 opposite the center of the screen 14 while the 50 having an aperture facing said reproduction and includtable 2 is moved relative to the image reproducing lens iiig means for producing an electrical force which varies elements. In this manner, the unit continually scans a with the intensity of light entering said aperture, means moving reproduction which 18 produced by the center for moving said unit and reproduction rectilineaily and portions of the image producing lens elements Somerelatively with respect to each other whereby the light what more accurate results may be obtained in this entering said aperture varies with the intensity of illumimanner since inaccuracies due to distortion at the edges natiOH from each PO111t 0f Sald reproduction along a line of lmages produced b l elements are li n d extending transversely thereof, and circuit means connect- Wbfl o e b d m t f my v m o ha b ing said electrical force producing means in said scanning how a d d ribed it will be apparent th t th unit with said electrical force responsive actuating means adaptations and modifications may be made without de- 40 in Said instrument.

I claim: References Cited in the file of this patent l. A method off determiiliing the metallloglraphic con- UNITED STATES PATENTS stituent content 0 a meta specimen w ic comprises producing an illuminated reproduction of an etched suri gg g 2 face of the specimen, and electrically scanning the inten- 2279646 Smith 1942 sity of illumination from each point of said reproduction n p 

2. A METHOD OF DETERMINING THE METALLOGRAPHIC CONSTITUENT CONTENT OF A METAL SPECIMEN WHICH COMPRISES PRODUCING AN ILLUMINATED REPRODUCTION OF AN ETCHED SURFACE OF THE SPECIMEN, ELECTRICALLY SCANNING THE INTENSITY OF ILLUMINATION FROM EACH POINT OF SAID REPRODUCTION ALONG A LINE EXTENDING TRANSVERSELY THEREOF TO PRODUCE ELECTRICAL INTELLIGENCE IN THE FORM OF AN ELECTRIC FORCE VARYING WITH THE INTENSITY OF ILLUMINATION ALONG SAID LINE, AND RECORDING THE VARIATIONS IN SAID ELECTRIC FORCE TO PROVIDE A RECORD OF MICROCONSTITUENTS OF SAID SPECIMEN. 